Transition metal dichalcogenide nanospheres for high-refractive-index nanophotonics and biomedical theranostics

Recent developments in the area of resonant dielectric nanostructures have created attractive opportunities for concentrating and manipulating light at the nanoscale and the establishment of the new exciting field of all-dielectric nanophotonics. Transition metal dichalcogenides (TMDCs) with nanopatterned surfaces are especially promising for these tasks. Still, the fabrication of these structures requires sophisticated lithographic processes, drastically complicating application prospects. To bridge this gap and broaden the application scope of TMDC nanomaterials, we report here femtosecond laser-ablative fabrication of water-dispersed spherical TMDC (MoS2 and WS2) nanoparticles (NPs) of variable size (5 to 250 nm). Such NPs demonstrate exciting optical and electronic properties inherited from TMDC crystals, due to preserved crystalline structure, which offers a unique combination of pronounced excitonic response and high refractive index value, making possible a strong concentration of electromagnetic field in the NPs. Furthermore, such NPs offer additional tunability due to hybridization between the Mie and excitonic resonances. Such properties bring to life a number of nontrivial effects, including enhanced photoabsorption and photothermal conversion. As an illustration, we demonstrate that the NPs exhibit a very strong photothermal response, much exceeding that of conventional dielectric nanoresonators based on Si. Being in a mobile colloidal state and exhibiting superior optical properties compared to other dielectric resonant structures, the synthesized TMDC NPs offer opportunities for the development of next-generation nanophotonic and nanotheranostic platforms, including photothermal therapy and multimodal bioimaging

What theranostic applications could ultrapure laser-synthesized Si nanoparticles have in cancer?

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Size-controllable synthesis of bare gold nanoparticles by femtosecond laser fragmentation in water

International audienceWe report a size-controllable synthesis of stable aqueous solutions of ultrapure low-size-dispersed Au nanoparticles by methods of femtosecond laser fragmentation from preliminary formed colloids. Such approach makes possible the tuning of mean nanoparticle size between a few nm and several tens of nm under the size dispersion lower than 70% by varying the fluence of pumping radiation during the fragmentation procedure. The efficient size control is explained by 3D geometry of laser fragmentation by femtosecond laser-induced white light super-continuum and plasma-related phenomena. Despite the absence of any protective ligands, the nanoparticle solutions demonstrate exceptional stability due to electric repulsion effect associated with strong negative charging of formed nanoparticles. Stable aqueous solutions of bare gold nanoparticles present a unique object with a variety of potential applications in catalysis, surface-enhanced Raman spectroscopy, photovoltaics, biosensing and biomedicine

Plasmonic resonances in diffractive arrays of gold nanoantennas: near and far field effects

International audienceWe examine the excitation of plasmonic resonances in arrays of periodically arranged gold nanoparticles placed in a uniform refractive index environment. Under a proper periodicity of the nanoparticle lattice, such nanoantenna arrays are known to exhibit narrow resonances with asymmetric Fano-type spectral line shape in transmission and reflection spectra having much better resonance quality compared to the single nanoparticle case. Using numerical simulations, we first identify two distinct regimes of lattice response, associated with two-characteristic states of the spectra: Rayleigh anomaly and lattice plasmon mode. The evolution of the electric field pattern is rigorously studied for these two states revealing different configurations of optical forces: the first regime is characterized by the concentration of electric field between the nanoparticles, yielding to almost complete transparency of the array, whereas the second regime is characterized by the concentration of electric field on the nanoparticles and a strong plasmon-related absorption/scattering. We present electric field distributions for different spectral positions of Rayleigh anomaly with respect to the single nanoparticle resonance and optimize lattice parameters in order to maximize the enhancement of electric field on the nanoparticles. Finally, by employing collective plasmon excitations, we explore possibilities for electric field enhancement in the region between the nanoparticles. The presented results are of importance for the field enhanced spectroscopy as well as for plasmonic bio and chemical sensing. (C)2012 Optical Society of Americ

Photoluminescence properties of silicon nanocrystals grown by nanosecond laser ablation of solid-state targets in an inert gas atmosphere

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HXG-039

Aerial Photograph of the greater Mankato Area, Mankato, Minnesota from 1959.https://cornerstone.lib.mnsu.edu/aerial_1959_HXG/1038/thumbnail.jp

Multi-layer si-based surface plasmon resonance structure for adsorption sensing

A multi-layer Si-based surface plasmon resonance (SPR) sensing structure, consisting of a silicon coupling prism, an intermediate SiO 2 layer, a gold film, and a sensing medium, is considered. Such structure makes possible an excitation of two angularly separated surface plasmon polariton modes over both sides of the gold film. We examine the response of the system in the case of the absorption sensing, which is simulated by the gold thickness change. Both calculations and experimental data show that the 'internal' plasmon mode over the SiO 2/gold interface appears to be at least 4-6 times more sensitive than the 'external' one over the gold/sensing medium interface, which is employed in most conventional SPR schemes. The proposed internal plasmon-based absorption sensor structure can be used for studies of optical absorption layers and for colloidal Au-enhanced SPR sensing of ultra-small (bio)-chemical agents.NRC publication: Ye

Particle-free inkjet printing of nanostructured porous indium tin oxide thin films

International audienceWe report a simple, low-cost, single-step inkjet printing method for the fabrication of nanostructured, highly transparent and conductive ITO films, which completely avoids the use of ITO particles in the fabrication process. In our method, the inks are formed from a liquid solution presenting a properly selected mixture of indium and tin acetates. After jet printing, the ink is decomposed during a subsequent annealing step, in which the released CO2 gas bubbles control the ITO nucleation process to provide a porous film texture. We show that the fabricated ITO films are highly crystalline, stoichiometric, and nanoporous with controlled porosity. Electrical measurements show relatively low resistivity values for the films (down to 0.029 Omega cm) comparable to those of the best ITO thin films fabricated by other methods. Optical ellipsometry tests demonstrate a relatively high refractive index (1.5-1.7) and high transparency of the films over a wide region of the spectrum ranging from 500 to 1700 nm. Since the method does not require any pre-fabricated ITO particles, masks or templates, and enables the deposition of films on substrates of various materials and shapes, it can be employed for fabrication of nanoporous ITO films for a diversity of applications, including solar cell, bio- and chemical sensing, etc